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flowrate at a wellhead vacuum of approximately 75 inches of water column would likely produce an effective ROI in excess of 80 feet An effective ROI of 80 feet will provide for the ability to extract residual TPHg beyond boring SB-17 Based on an effective ROI of 80 feet at a flowrate of 100 scfm, using VW-I as the vapor extraction well should provide sufficient vacuum influence for the entire on-site vadose zone and capillary fringe zone impacted soil plumes Designing the VES based on a flowrate of 100 scfm, rather than a lesser flowrate, is recommended to provide sufficient remedial coverage of the entire impacted soil ' areas ' Vapor samples collected during the VET were analyzed for TPHg and BTEX in order to evaluate the expected mass removal rate for a soil VES Calculations indicate that at an extraction rate of 100 scfm, approximately 1,000 pounds per day(ppd) of TPHg could be extracted from well VW-I at the time of VES start-up Based on the expected start-up TPHg vapor concentrations in excess of 125,000 mg/m3, a thermal oxidizer (therm-ox) will provide for the most economic treatment and ' atmospheric discharge of extracted soil gas At VES start-up, the maximum daily extraction rate will be limited by the maximum TPHg concentration that the selected therm-ox can process Typical ' maximum process concentrations range from approximately 7,500 ppm to 10,000 ppm (33,400 mg/m3 to 44,600 mg/m3)and are manufacturer specific Because the expected TPHg concentration in soil gas at the time of VES start-up will exceed the maximum process capacity of a therm-ox, extracted soil gas will initially require atmospheric ' dilution to reduce the influent concentration to approximately 7,500 ppm to 10,000 ppm Therefore, the total system process capacity for a 100 scfm VES (assuming therm-ox inlet TPHg concentrations of 33,000 mg/m3) is expected to be approximately 300 ppd 1 ProjectNo 58100-06-18A -12- December 9, 1996